A 2200-yr record of hydrologic variability from Foy Lake, Montana, USA, inferred from diatom and geochemical data

Abstract

A 2200-yr long, high-resolution (∼5 yr) record of drought variability in northwest Montana is inferred from diatoms and δ18O values of bio-induced carbonate preserved in a varved lacustrine core from Foy Lake. A previously developed model of the diatom response to lake-level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data. High-frequency (decadal) fluctuations in the de-trended δ18O record mirror variations in wet/dry cycles inferred from Banff tree-rings, demonstrating the sensitivity of the oxygen-isotope values to changes in regional moisture balance. Low frequency (multi-centennial) isotopic changes may be associated with shifts in the seasonal distribution of precipitation. From 200 B.C. to A.D. 800, both diatom and isotope records indicate that climate was dry and lake level low, with poor diatom preservation and high organic carbon: nitrogen ratios. Subsequently, lake level rose slightly, although the climate was drier and more stable than modern conditions. At A.D. 1200, lake level increased to approximately 6 m below present elevation, after which the lake fluctuated between this elevation and full stage, with particularly cool and/or wetter conditions after 1700. The hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake's outlet. Spectral analysis of the δ18O data indicates that severe droughts occurred with multi-decadal (50 to 70 yr) frequency.

A regional-scale climate reconstruction of the last 4000 years from lakes in the Nebraska Sand Hills, USA

“…Although this inference is based on a limited number of sites, the increased moisture during the last ~1300 a in Westernmost Nebraska resembles the pattern evident in lacustrine high-resolution records of drought variability from the northern Rocky Mountain region, an area that is more strongly influenced by Pacific moisture sources. At Foy Lake in eastern Montana, consistently lower lake-levels occurred between 2300 and 1300 cal a BP and generally higher lake-stands were present between 1300 cal a BP to the present (Stevens et al, 2006). Similarly, two lake records in the Beaverhead Mountains of western Montana, as well as Crevice Lake in Yellowstone National Park, showed higher effective moisture after ~1300 cal a BP (Bracht et al, 2008;Bracht, 2010).…”

A 2650-year-long record of environmental change from northern Yellowstone National Park based on a comparison of multiple proxy data

“…1300 and 650 cal yr BP (AD 650-1300) in the western US and Great Plains (e.g., Case and MacDonald, 2003;Fritz et al, 2000;Laird et al, 1996;Pierce et al, 2004;Stevens et al, 2006;Woodhouse and Overpeck, 1998). The local PDSI data show persistent dry conditions between 1200 and 900 cal yr BP (AD 750-1050), followed by an interval of alternating wet and dry extremes from 900 to 600 cal yr BP (AD 1050-1350).…”

Synchronous climatic change inferred from diatom records in four western Montana lakes in the U.S. Rocky Mountains

“…Foy Lake shows a spike of C. halophila at approximately 625 cal yr BP. Stevens et al (2006) interpret this benthic spike as a modest rise in lake level. Thus, Crevice, Morrison, and Reservoir lakes show evidence of a transition to protracted cool springs and shorter summers, while Foy Lake shows a moderate increase in effective moisture, which similarly could be a product of lower spring and summer temperatures or could reflect an increase in precipitation.…”